To reduce loss of heat due to thermal cycling, it is desirable to minimise the thermal mass of the base, for example as described in our European Patent specification No. 0024037. This shows a kiln car base structure formed from a plurality of upright pillars which are carried by the trolley, the pillars serving to locate and support vertically extending ceramic plates which form a wall around at least the periphery of the base so as to define one or more compartments which contain low thermal capacity insulating material. In this prior construction, the pillars each comprise a plurality of vertically stacked elements of load-bearing, thermally insulating ceramic material, and in order to provide a radiative heat seal around the periphery of the base, horizontally disposed generally flat ceramic bats are mounted between a pair of adjacent pillar elements, and extend peripherally outwardly beyond the pillars and the vertical wall plates. Kiln cars of this kind are described in U.S. Pat. Nos. 4,462,798 and 4,721,459.
A further lightweight base structure is disclosed in our British Pat. No. 2179127 in which the pillars which provide support for vertical wall plates are each formed from a single refractor member and the radiative heat seal is afforded by a generally T-section element which is located with the web thereof extending horizontally between a pair of vertically spaced wall plates which define the outer periphery of the hollow base structure.
Both these arrangements have their disadvantages. Forming the pillars from stacked elements provides less rigid support for the superstructure than might otherwise be the case, and interposing the heat seal bat between such pillar elements requires the bat to be constructed as a load bearing member and experience has shown that in use such bats are prone to fracture adjacent to the pillars. Forming the pillars as single refractory members is advantangeous, but the T-shaped heat seal bat is relatively difficult to manufacture successfully, and it is also difficult to assemble with the vertical wall plates.